class_docstr: TorchRankerAgent implementation of the biencoder.
  
  It is a standalone Agent. It might be called by the Both Encoder.
code: def dictionary_class():
      return BertDictionaryAgent
  
imports: from typing import Optional
  from parlai.core.params import ParlaiParser
  from parlai.core.opt import Opt
  from parlai.core.torch_ranker_agent import TorchRankerAgent
  from parlai.utils.torch import padded_3d
  from parlai.zoo.bert.build import download
  from parlai.utils.io import PathManager
  from .bert_dictionary import BertDictionaryAgent
  from .helpers import BertWrapper, BertModel, add_common_args, surround, MODEL_PATH
  import os
  import torch
  from tqdm import tqdm
label_desc: Use image node_id 4 for calling the BiEncoderRankerAgent obj's underlying member method code with example usage: obj.dictionary_class() and returns: BertDictionaryAgent